Very neat studio space. I think it is the widely accepted idea to paint the walls as close to 18% grey as you can get. That will give you the option to shoot with the wall directly behind the subject, and you can use a gelled flash to create the color. Doing so will make it much easier to shoot a quick headshot, as you will not have to pull out the backdrops and stands for a couple simple shots.
For the floor, honestly that is up to you, however if I were building a studio, I would probably use a hardwood (or faux-hardwood) floor, as opposed to carpet, because it is much easier to roll a light stand on casters around a hard flat surface than a soft, carpeted floor. Also a nice looking floor gives a very professional feel to the place no matter what dull shade of grey the walls are. 